Scintillation cameras or gamma cameras are well known in the art and are used primarily in medical diagnostics for obtaining images of the internal organs or tissues of a patient who has ingested a trace amount of a radioactive isotope. The conventional construction for such cameras is to provide an array of highly sensitive photomultiplier tubes which are optically coupled to a scintillation crystal which will create a small flash of light in response to interaction with incident gamma rays. Each tube has a relatively large surface area, namely greater than 30 cm.sup.2, and therefore to determine the exact position of a scintillation, means are used to calculate the position based on intensity values from at least three photomultiplier tubes. Obviously, the accuracy of the calculated positions of the events is strongly dependent on the accuracy of the gain calibration of each photomultiplier tube. Small errors in gain calibration will cause blurring or distortion in the medical diagnostic image.
It is therefore an object of the present invention to provide a method and apparatus which will quickly carry out a gain calibration for each photomultiplier tube in order to improve the quality of the resulting images. It is furthermore an object of the present invention to provide a method and apparatus for carrying out a gain calibration in a scintillation camera which does not add substantially to the cost of the camera system.